Differential Diagnosis in Neurology

Topic 16. Dementia

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General considerations:
- Microglial and macrophage cellular CNS reservoir of infection
- Cytokine and protein effectors of cell death
Clinical features:
- May affect majority of untreated patients
- May be presenting feature of the illness
- Forgetfulness
- Poor concentration
- Subcortical dementia
- Later features:
  - Increasing psychomotor slowing
  - Ataxia
  - Paraparesis
  - Early cognitive changes in asymptomatic HIV patients
Laboratory evaluation:
- Increased lymphocytic pleocytosis
- Protein usually mildly elevated to 50 mg to 80 mg%
MRI evaluation:
- Global atrophy of both grey and white matter atrophy
- Basal ganglionic atrophy
- Diffuse white mater increased signal on T2 weighted images (primarily periventricularly)
Pathology:
- Diffuse white matter change
- Subcortical gray matter
- Relative sparing of the cerebral cortex
- Macrophages, multinucleated cells and reactive gliosis of affected areas
- Associated pathologic processes:
  - Lymphoma
  - Progressive multifocal leukoencephalopathy
  - Infections:
    - Toxoplasmosis
    - Tuberculosis
    - Syphilis
    - Cryptococcus
    - Herpes simplex
    - Herpes varicella zoster
    - Epstein Barr

General considerations:
- Subacute sclerosing panencephalitis (SSPE):
  - Most often follows late immunization with measles vaccine
  - Overwhelming a childhood disease
  - Adult form has been described
Clinical features:
- School failure (earliest cognitive signs)
- Apraxia
- Visual spatial difficulties
- Myoclonus
Pathology:
- Dawson's inclusion bodies:
  - Cowdry A bodies
  - Large intranuclear inclusions with halo
  - Viral (DNA) infections
Laboratory evaluations:
- Positive IgG index >7%/100 ml
- Slightly raised protein
- Few lymphocytes

General considerations:
- Usually occurs after congenital infection; may follow acquired infection in adult
Clinical features:
- Early cerebellar findings
- Lack of myoclonus
Pathology:
- Neuronal destruction in cortex, cerebellum, brainstem
- Perivascular lymphocytic infiltration
- Myelin destruction, axonal sparing
Diagnostic evaluation:
- Early cerebellar findings
- Lack of myoclonus

General considerations:
- Occurs in all immunocomprised conditions:
  - HIV
  - Renal failure
  - Malignancy
  - Liver disease
- Chronic infection with JC virus
Clinical features:
- Cognitive impairment
- Ataxia
- Hemiparesis
- Hemianopsia and central visual loss
- Parietal sensory loss
- Rare brainstem signs and symptoms
- A few patients with remissions and long survival
Pathology:
- Serpiginous coalescent white matter lesions:
  - Parietooccipital origin
- Large bizarre multinucleated oligodendrocyte (intranuclear occlusions)
- Confluent foci of demyelination

General considerations:
- Telescoped pattern of infection:
  - Primary, meningoencephalitic pattern may develop concomitantly
  - Neurosyphilis may develop although primary infection was adequately treated
  - Usual treponemal antibody tests may be negative
Clinical features:
- Ocular involvement is prominent
- Syphilitic meningitis is common
- Gummatous arteritis occurs
- Fulminant necrotizing hyperinfections anergic stage (quaternary syphilis)

General considerations:
- Gastrointestinal malabsorption syndrome
- Large joint arthritis
Clinical features:
- Disease of middle aged men (4–6 decade)
- Neurological signs and symptoms may occur without systemic features
- Neurologic involvement may be silent:
  - Only found at autopsy
- Dementia
- Myorhythmia (side to side jaw movement)
- Ophthalmoplegia
- Ataxia
- Hypothalamic syndrome
- Lymphadenopathy
- Hyperpigmentation
- Steatorrhea
- Associated with AIDS
Pathology:
- Abnormal macrophages (Whipple's bacilli) noted on jejunal biopsy
- Rod shaped bacilli; gram positive actinomycete (Trophermyma Whipple)
- Disseminated lesions throughout the CNS; subpial regions of the cortex, basal ganglia, hypothalamus, dentate, brainstem nuclei
- Small infarcts (less than 5 mm) scattered throughout the brain

General considerations:
- Most common helminth with CNS involvement
- Significant problem in immigrants to North America
- Seen in 1–3% of post mortem studies in Mexico
- Unusual in non-pork eating countries
- Infection caused by the larval stage of the pig tapeworm taenia solium
Clinical features:
- Seizures
- Acute or focal neurological signs
- Raised intracranial pressure
- Hydrocephalus
- Meningeal form
- Involves the diaphragm
- Muscle enlargement from inflammation
- Chronic dementia from the severe lesion load
Pathology:
- Most cysts are parenchymal; vary from one to several hundreds
- Cysts are found:
  - Cortex
  - Deep grey nuclei
  - White matter
  - Cerebellum
  - Meninges
  - Ventricles
- Racemose variety may occlude internal carotid artery or burst in a ventricle that causes meningitis
MRI evaluation:
- Calcified and non-calcified cysts
- Meningeal and ventricular involvement in some patients
- Racemose (cystic involvement of IVth ventricle)